In the past, I have been a very accuracy focused shooter. While certainly not the most accurate, I place a lot of value in being able to get really solid hits. Because of that, I prefer a very precise sight picture, with the fired round hitting to the top of the front blade. This allows for more precise placement of the round on the target because I can see where the round will actually impact.
The problem is not all manufacturers agree with me (surprise, I know). Some manufacturers use what is commonly called a “drive the dot” sight picture. Meaning the round will impact the target where the dot on the front sight is, not where the top edge of the sight is.
It just so happens FN uses this sight picture. From a practical perspective, that means I am having to focus on two parts of the front sight. I have to watch the top edge and sides to ensure I get proper alignment, and then also pay attention to where the dot on the front sight is located on the target. Failing to do so will cause the gun to shoot below the intended point of impact.
Quite honestly, I am not accustomed to that process, and it will take me time to adapt. It still requires a conscious effort to ensure I utilize the correct sighting technique. While I understand this method of sighting is not uncommon, it is annoying to deal with until I can put aftermarket sights on the gun. Trying to get the same level of precision using a “drive the dot” style of sighting has certainly been a challenge.
If there was one consistent complaint I have about the 509, it would be the sights in one way or the other. The are large and chunky, use a POA/POI system that makes it difficult to wring out all of the accuracy and precision available in the gun, and they are regulated for a 15 yard zero instead of a 25 yard zero. That being said, they are at least mostly serviceable from the factory, unlike some other manufacturers that like to put plastic sights on their guns.
Priority: Performance 
If I were you, I’d grab a file and give a few strokes to the top of the front sight. Not down to the middle of the dot, but just a few thousandths of an inch off the top and see where that changes the POI. Since you’ll have to bring the front of your slide up just a hair more, the POI will move up from your front dot. Rinse & repeat until the bullets hit where you want them. Be careful not to take too much off, it’s hard to file it back 🙂
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I have debated it. Supposedly the dovetails are the same as used on Sig pistols, so I will likely just change the sights all together. Dawson Precision is my usual go to, I just wanted to offer some material on using the factory sights since it seems absent from other sources before I make a switch.
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Finding a factory option that suits your needs may be a better solution than tuning the sights yourself.
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